This invention relates to a closure mechanism for folding flexible sheets of foil around the rim portion of a container. More particularly, the mechanism is used for closing covers of food tray containers such as are used for TV dinners. These containers are filled with food and covered with a flexible cover sheet of foil.
The apparatus of this invention is used in conjunction with an assembly for covering rimmed tray containers with foil sheets such as are disclosed in U.S. Pat. Nos. 2,889,675 and 2,948,096. Each of these patents discloses a mechanism for folding a flexible cover sheet around a leading rim portion and two opposing side rim portions with a subsequent folding apparatus for folding the trailing edge of the foil sheet as shown in those patents.
In U.S. Pat. No. 3,116,580, a single element is used to tuck and fold the trailing edge of a flexible cover sheet around the rim structure of a tray container. A basic disadvantage found associated with this structure is that the cover sheet, generally aluminum foil, is crushed against the under portion of the trailing rim. That is, there is a bunching effect and never any uniformity with regard to the folding of the foil around the rim structure. Without a neat folded configuration, the cover sheet is not tightly fitted in any uniform manner. Due to the non-uniformity and irregularity of the final folding operation, the sealing characteristics of the cover sheet over the tray container are therefore adversely affected.
Another problem found associated with such a crushing fold is related to the use of very thin foil sheets. Where thicker foil is used, the tightness of the fold depends somewhat upon the strength of the foil material itself. That is, a foil material having a one mil thickness is going to wrap more tightly than a foil having a thickness of about 0.0005 inch. It therefore becomes very important that a neat fold is effectuated along each side of the rimmed tray container because the residual strength of the thinner foils is not as effective in attaining the tightness of the seal around the rim of the container.